Laser disinfection of fluids

ABSTRACT

The disinfection of water or other fluid is accomplished by passing a stream of the fluid through a laser beam which radiates light in the ultraviolet range. A gas pulsed laser is disclosed which produces a beam having a substantial width and depth and a measurable length, as measured in the direction of fluid flow. The laser is positioned out of contact with the stream but with its beam filling the cross-section of the stream of water which can flow through a flume or over a weir. Flow meters are provided which adjust the rate of pulsing of the laser, and therefore the intensity of the ultraviolet light, in relation to changes in flow. Sensors are also provided to adjust the intensity of the laser for changes in turbidity or organic content of the fluid. In one embodiment the fluid flows through a spiral tube which directs the fluid to and fro through the laser beam. In another embodiment, the length of the laser beam is adjusted by adjusting the distance between the laser beam source and a diverging lens. The laser beam may be reflected off of mirrored surfaces, and utilizes the scattering of the ultra-violet light produced by suspended particles in the fluid being treated.

This is a divisional application of application Ser. No. 571,228, filedJan. 16, 1984, abandoned.

BACKGROUND OF THE INVENTION

This invention relates to a method and apparatus for disinfecting water,and more particularly to such an apparatus and method which employultraviolet light generated by a laser.

Ultraviolet light is a known disinfection agent for water. It has beentypical in the past to provide a series of banks of ultraviolet lightbulbs and to flow the water to be treated over the surfaces of thebulbs. There are a number of disadvantages to this approach. First, theintensity of the ultraviolet light varies with the distance from thesurface of the bulbs. Therefore, the bulbs must either be very closelyspaced or special bulb arrays must be used which provide sufficientintensity of the ultraviolet light for all water flowing past the bulbs.Even then, the flow past the bulbs must be relatively slow so that anadequate dosage of the ultraviolet light is likely to result. The closespacing of the bulbs results in considerable head loss. Secondly, thebulbs have a tendency to become coated or clouded thereby reducing theintensity of the ultraviolet light. One approach to overcoming thisproblem has been to provide apparatus which allows for periodic removaland cleaning of the bulbs so as to minimize the loss due to coating. Asecond approach to the coating problem has been to provide anultraviolet light intensity which is greater than initially needed sothat the intensity will still be adequate even after the bulbs becomecoated. Thirdly, bacteria which are supported by suspended particles maynot be exposed to the ultra-violet light if it is shielded from thelight source by the particle.

There are sources of ultraviolet light in addition to the bulbs or lampsnow commonly used for disinfection. One source is a laser which, byproper selection of the lasing gas, can be caused to radiate light inthe ultraviolet range. The use of laser generated ultraviolet light hasnot been heretofore proposed for the disinfection of wastewater. Thelaser has decided operating advantages, including the ability to haveits intensity, controlled in relation to operating conditions, such asflow rate, or characteristics of the water or other fluid being treated,such as turbidity or organic content. The geometry of the beam is alsocontrollable to adjust for changing in operating conditions or fluidcharacteristics, The laser is capable of generating high intensityultraviolet light and allows for faster velocities of the water, reduceshead loss, will tolerate higher turbidity in the water and reduce thepossibility of bacteria not being exposed to the ultraviolet light.

I have found ways in which to efficiently and effectively utilize thelaser in the disinfection of water. By disinfection is meant the abilityof a laser radiating in the ultra-violet spectrum to kill bacteriaprimarily by direct contact rather than by secondary photochemicaleffects. While these secondary effects might have the effect of killingthe bacteria they can also lead to a reactivation of the bacteria whichwill have a negative effect on the disinfection process. Although mymethod and apparatus is particularly adapted for the treatment of water,it can also be employed to disinfect fluids generally, including thosewhich are water based and those which are not, and including gases suchas air.

SUMMARY OF THE INVENTION

In the broadest sense, my invention involves a method and apparatus fordisinfecting a fluid which involves passing a stream of the fluidthrough a laser beam which radiates light in the ultraviolet range. Myinvention is particularly adapted for the disinfection of water and forthe use of a gas pulsed laser whose rate of pulse and therefore averageintensity of light can be adjusted. The pulse rate may vary from slow toso rapid as to be an essentially constant beam. The rate of pulse isadjusted for changes in the rate of flow of the stream of fluid passingthrough the laser beam and can also be adjusted for changes in theturbidity of water being treated so that the intensity of theultraviolet light can be controlled to match that which is needed byconditions of operation or conditions of the fluid being treated.

Further in accordance with the invention I provide method and apparatusfor varying the rate of flow of the stream of fluid while maintaining aconstant intensity of the ultra-violet beam.

A laser beam in accordance with my invention has a substantial width andthe stream is passed through the essentially stationary beam. Thecross-section of the stream can be selected to correspond to the area ofthe beam or to take advantage of the effects of scattering of the lightas the beam encounters suspended particles.

Still further in accordance with the invention I provide a method andapparatus for reflecting the beam off of a surface or surfaces of thecontainer for the stream of fluid, or off of the surface of the streamitself. The reflection and scattering from the container surface is usedto confine the spreading of the beam due to suspended particles in thefluid, and to decrease the beam cross-sectional area to compensate foralteration of the beam so as to maintain a nearly uniform intensityalong the length of the region in which the beam and stream interact.

In one embodiment of the invention, I provide for adjustment of theangle of penetration of the beam with respect to the stream in responseto changes in the turbidity of the fluid.

More particularly, in accordance with my invention I provide a method ofdisinfecting water which comprises the steps of providing a stream ofwater to be treated, generating a pulsed gas laser beam which radiateslight in the ultraviolet range, and directing the laser beam into thestream of water. The method may include the additional steps ofincreasing the rate of the pulses of the laser bam in proportion to anincrease in the rate of flow of water in the stream or in proportion toan increase in the turbidity of the water in the stream. The methodpreferably includes the step of sensing the amount of visible lightscattered by suspended particles in the water as the method by which therate of pulses of the laser beam is varied relative to changes inturbidity. The method may also include the step of altering the geometryof the laser beam, and particularly its length, in response to changesin fluid characteristics, such as organic content.

I also provide an apparatus for disinfecting water by th exposure of thewater to light in the ultraviolet range which includes a water containerhaving an inlet and an outlet, means for controlling the cross-sectionof the water flowing between the inlet and the outlet, and a pulsed gaslaser having its beam filling the cross-section of the water andradiating light in the ultraviolet range. The apparatus may also includemeans for sensing the visible light scattered by suspended particles inthe water and for regulating the operation of the controlling means toreduce the cross-section of water as the amount of sensed visible lightincreases. The apparatus may also include means for controlling the rateof the pulses of the laser and flow responsive means in the containerwhich regulate the operation of the pulse rate control, or means forsensing the visible light reflected by suspended particles in the waterand for regulating the operation of the pulsed rate control in responseto the amount of visible light. The apparatus may also include means forchanging the length of the laser beam (as measured in the direction offluid flow) in response to sensed change conditions of the fluid.

The container may take the form of a flume or a weir. In either event,the laser beam is directed transverse of the stream of water. The streammay be so shaped either by varying the width of the flume or theelevation of the weir that the cross-section of the stream matches theshape of the beam which diverges as it passes through the wastewater.The stream may also be so shaped that its cross-section narrows tocompensate for alternation of the beam in turbid fluids.

It is a principal object of this invention to provide an effective andefficient method and apparatus for disinfecting water and other fluidsby the use of ultraviolet light which does not involve contact with thefluid with the source of the ultra-violet light.

It is a further object of the invention to provide a method andapparatus for varying the ultraviolet light intensity of a source inresponse to operating conditions such as flow rate and in response toconditions of the water or fluid such as the turbidity.

It is yet another object of the invention to provide a gas pulsed laserapparatus which has provision for controlling the pulse rate of thelaser in response to changes in turbidity or rate of flow of the streamof fluid being treated.

The foregoing and other objects and advantages will appear in thedescription which follows. In the following description of the preferredembodiments, reference is made to the attached drawings which form apart hereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view in perspective, with portions broken away for clarity,of a pulsed gas laser which is usable in the praactice of the invention;

FIG. 2 is a top plan view, partially schematic, of the laser of FIG. 1;

FIG. 3 is a partial view similar to FIG. 2 but showing alternatemechanisms and circuits for controlling the spark gap switch and voltagesource;

FIG. 4 is a view in perspective of a flume arrangement for disinfectionof a fluid using the laser of FIGS. 1-3;

FIG. 5 is a view in longitudinal section of the flume of FIG. 4;

FIGS. 6 and 7 are cross-sectional views of alternate shapes of the flumeof FIG. 5;

FIG. 8 is a view in perspective of a weir arrangement for thedisinfection of wastewater using the laser of FIGS. 1-3;

FIG. 9 is a view in longitudinal section through the weir of FIG. 6;

FIG. 10 is a partial view in transverse section viewed along the weirbut showing an alternate arrangement for the elevation of the weir;

FIG. 11 is a view in cross-section of a spiral tube container fortreating a stream of wastewater by means of the laser of FIGS. 1-3;

FIG. 12 is a view in elevation of the spiral tube of FIG. 9.; and

FIG. 13 is a partial view in elevation of a modified form of theapparatus of FIGS. 4 and 5 which provides for adjusting the geometry ofthe laser beam.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIGS. 1-3, a laser 10 is illustrated which is amodification of a pulsed gas laser of the type described in U.S. Pat.No. 3,757,248 issued Sept. 4, 1973 to Small for "Pulsed Gas Laser". Thelaser includes a pair of electrodes 11 and 12 each of which constituteone plate of a capacitor. The electrodes 11 and 12 are arranged onrespective inner surfaces of a pair of dielectric plates 13 and 14,respectively, which are mounted parallel to each other and which aresecured on opposite sides of a chamber assembly formed of chamber halves15 and 16. The chamber halves 15 and 16 together define a chamber cavity17 which is oval shaped and which extends longitudinally of the chamberassembly. The electrodes 11 and 12 are turned toward each other withinthe chamber 17 so that the respective electrode ends 18 and 19 confronteach other and are spaced apart within the chamber 17. The chamber isconnected to an evacuation pump 20 and is fed by a source of gas 21which may be a pressure cylinder operating through a regulator valve 22.

A pair of conductive plates 25 and 26 are formed on the opposite,outside surfaces of the dielectric plates 13 and 14, respectively. Bothof the conductive plates 25 and 26 are connected to ground. Theelectrode plates 11 and 12 are connected to each other through aninduction coil 27 and the electrode plate 12 is connected to a highvoltage d.c. source 28 through an induction coil 29. The high voltaged.c. source 28 will charge the electrode plate 12 and will thereaftercharge the electrode plate 11 through the coil 27. A spark gap switch 30is connected to the electrode plate 11 and will ground that plateperiodically when the spark gap switch arcs. The sudden grounding of theelectrode plate 11 will produce a very high potential across the gapbetween the electrode ends 18 and 19 such that electrons will flowbetween the ends. If the chamber is filled with a lasable gas such asnitrogen, the flow of electrons will cause lasing and a laser beamhaving a substantial width will result. The beam is illustrated in FIGS.1 and 2 in phantom lines and is identified by the reference numeral 31.By the proper selection of the gas, the laser 10 will produce a beam 31which radiates light in the ultraviolet range. Nitrogen is one such gas.The beam has a significant width (W) and a significant depth (D). Thesmallest dimension of the beam which will be called its length (L), isalso measurable and can be manipulated to advantage, as will appearhereafter. The terms "length" is used because it is the dimension whichdescribes the length of time that fluid will be exposed to the beam. Theshape of the beam, that is one having a significant width, is incontrast with the typical laser beam which is a small diameter beam oflight.

In a laser 10 usable in my invention, the exciting voltage produced bythe high voltage source 28 may be in the magnitude of 30,000 volts witha gas pressure within the chamber 17 of 100 torr. This would produce alaser beam 31 which is about an inch wide and two feet in length.

The spark gap switch 30 can be periodically actuated to arc by use of anoscillator 35 in a known manner. In my invention, the rate of arcing ofthe spark gap switch and therefore the rate of pulsing of the laser 10is adjusted for conditions of operation and conditions of the fluidbeing treated. That variation can result from the oscillator 35 beingcontrolled by a photocell 36 which senses, as will be described ingreater detail hereafter, the turbidity of the fluid being treated. Analternative arrangement for controlling the pulsing of the laser isshown in FIG. 3.

In FIG. 3, the high voltage d.c. rectifier 28' is connected to an a.c.source through a potentiometer 37 which is adjusted by an analogcontroller 38 in response to the amount of light sensed by the photocell36. Changes in the amount of light sensed will therefor be reflected inchanges in the amperage to the high voltage d.c. rectifier 28' and thiswill have the effect of adjusting the speed at which the plates 11 and12 will be charged. Different charging speeds will produce differentrates of pulsing the laser.

FIG. 3 also illustrates a mechanism to adjust the spark gap as theelectrodes of the spark gap switch wear away. One contact 39 of thespark gap switch 30' is mounted on the end of a threaded rod 40 which isheld in a threaded block 41 and which mounts a pinion gear 42. Thepinion 42 meshes with a gear 43 mounted on the output shaft of the motor44 which is controlled by a motor controller 45 responsive to the outputvoltage of the high voltage source 28'. As the spark gap increases dueto electrode wear, the charging voltage to arc the spark gap will alsoincrease. This is sensed by the motor controller 45 which causes themotor to move the contact 39 closer to the fixed contact to reduce thegap. Therefore, a predetermined charging voltage to the laser ismaintained thereby insuring consistent laser pulses at discharge.

Referring to FIGS. 4 and 5, the laser 10 is shown mounted in relation toa flume structure indicated generally by the reference numeral 50. Theflume 50 includes a container having a pair of upright side walls 51 and52. The side walls are flared at both ends to form an inlet portion 53and an outlet portion 54 communicating with respective inlet and outletpipes 55 and 56. Between the flared ends, the side walls 51 and 52 areparallel and define an area of constant cross-section. Baffle plates 57are disposed opposite the inlet and outlet pipes 55 and 56. A dam 60fills the cross-section of the flume 50 and is mounted at its top on anaxle 61 held in bearings 62 disposed on the opposite tops of the sidewalls 51 and 52. A counter weight 63 projects above the axle. The damwill control the flow of water through the flume and will be pivoted inthe event of significant changes in the rate of flow. The dam 60maintains the water depth in the flume and keeps the distance which thebeam travels through the air to a minimum. The distance between thelaser 10 and the surface of the water is exaggerated in the drawings.The laser 10 is mounted at the top of the flume 50 and has its laserbeam projecting downwardly into the water passing through the flume. Amirrored surface 65 is disposed along the bottom of the flume and isarranged to reflect the laser beam.

The laser beam fills the constant cross-section of the flume 50 so thata stream of water flowing through the flume will be passed through thebeam and all of the water will be exposed to the beam. The exposure tothe ultraviolet light will disinfect the water by contact kill of thebacteria in the water. Since the total dosage of the ultraviolet lightis important, the intensity of the laser beam is preferably adjusted toreflect the changes in the rate of flow of water passing through thebeam. The intensity of the laser beam is controllable by adjusting thepulse rate of the laser. This can be accomplished by adjusting theoscillator 35 or the potentiometer 37.

In the embodiment of FIGS. 4 and 5, the dam 60 will respond to the flowof water through the flume and its angle relative to the vertical willchange as flow changes. That is, the greater the flow the further thedam will be moved away from vertical. This change in position of the dam60 is sensed by a resolver 66 which is connected to the axle 61 for thedam. The resolver 66 can then send a signal to the oscillator 35 orpotentiometer 37 to thereby vary the rate at which the laser 10 ispulsed. For greater flow rate, the laser must be pulsed at a faster ratesince there will be a reduction in the time of exposure to the laserbeam.

Instead of the dam 60 and resolver 66, the flow rate may be sensed bythe use of a known sonic depth meter which will measure the depth ofwater in the flume. The depth is proportional to the flow rate and thedepth meter could be used to send a signal to the oscillator 35 orpotentiometer 37.

I have determined that the efectiveness of the disinfection of a fluid,and particularly water, by the use of laser generated ultraviolet lightis particularly sensitive to the turbidity of the fluid. It appears thatsuspended solids have the effect of reflecting and scattering the laserbeam. Since the laser beam must penetrate a significant depth of thewater, high turbidity will result in those portions of the water streamwhich are relatively remote from the entry point of the laser beam intothe stream receiving low levels of ultraviolet light because the beamwill have been significantly dispersed and scattered by the time itreaches the remote points. Thus, it is very desirable to increase theintensity of the laser beam whenever the turbidity increases. Theincreasing turbidity can be sensed by the use of a photoelectric cellsensor which, as illustrated in FIG. 5, is trained at the reflectedlaser beam and is responsive to the amount of light which is reflectedback up toward the surface. The less the light, the greater theturbidity. Alternatively, a similar photoelectric cell can be trainedsimply at the surface of the water and can be responsive to the amountof visible light which is reflected and scattered by suspended particlesin the water. In that case, the greater the amount of suspended solids,the greater will be the light sensed. In either case, the photoelectriccell is used to control the oscillator 35 or potentiometer 37 andthereby control the pulse rate of the laser 10.

Instead of adjusting the pulse rate as changes in turbidity are sensed,the angle of entry of the laser beam into the stream of water can alsobe adjusted in accordance with changes in turbidity. Thus, the laser 10of FIG. 5 is mounted at one end on a pivot shaft 68 held in bearingblocks mounted on the tops of the side walls 51 and 52. A sector gear 69is mounted on the laser 10 with its center of generation located at thepivot shaft 68. A pinion 70 engages the teeth of the sector gear 69 andthe pinion is driven by a motor-reducer 17 responsive to signals from aphotocell. For greater turbidity, the laser beam 10 would beautomatically positioned by rotation of the pinion 70 in response tosensed light to a position in which the beam is more nearly vertical sothat the beam reflected off the bottom will penetrate upwardly somedistance and the area of least beam intensity will therefore besubjected to a double pass of the beam along the same path.

The embodiment of FIGS. 4 and 5 uses a separate flow meter in the formof a dam 60 and resolver 66 and a separate turbidity sensor in the formof the photocell 67. If the laser disinfection apparatus is installed aspart of a larger waste-water treatment facility, which would typicallybe the case, the facility will have flow meters and turbidity metersused to control other portions of the treatment process. Those existingflow meters and turbidity meters can also be used to control theoperation of the laser in accordance with this invention.

There are other conditions of the fluid being treated which can besensed and can be used to control the intensity of the laser beam. Forexample, there are known Total Organic Carbon meters which give aninstantaneous reading indicative of the organic content of the water orother fluid. The organic content may be related to the turbidity or thebacteria content. The instantaneous reading from the Total OrganicCarbon meters can be converted into a signal which controls the pulserate of the laser in the same manner as the photocell 67 or resolver 66or other sensor of a condition or characteristic of the fluid.

In the arrangement of FIGS. 4 and 5, the side walls 51 and 52 of theflume are upright and are parallel at the narrowed center portion of theflume. In reality, the laser beam will have a tendency to become wideras it passes through the water being treated. If the intensity of theultraviolet light is sufficiently high and the turbidity of the water orother fluid being treated is sufficiently low, the tendency of the beamto widen as it passes through the fluid can be used to advantage. Thus,as illustrated in FIG. 6, the flume may be formed with a central portionin which the side walls 72 and 73 are spaced wider apart at the base ofthe flume then at the top. A greater-cross-section can be achieved bythat arrangement and therefore a greater quantity of water or otherfluid can be treated per unit of time.

In very turbid wastewater, the intensity of the ultra-violet light islikely to be so diminished by scattering from the suspended particlesthat by the time it reaches the bottom of the stream it will have verylittle, if any, ability to kill bacteria. A container having across-section illustrated in FIG. 7 can be used to maximize theuniformity of the intensity of the ultra-violet light throughout thedepth of the stream. In FIG. 7, the side walls 74 and 75 of the centralportion of the flume are spaced closer together at the bottom of theflume than at the top thereby forming a Williamson cone. The scatteringeffect caused by the suspended particles will have a tendency in thearrangement of FIG. 7 to focus the beam towards the bottom. Thistendency can be greatly enhanced by providing mirrored surfaces on allof the interior surfaces of the container. Thus, in the embodiment ofFIG. 7 the surfaces 74' and 75' would be formed of a reflective materialsuch as sheet aluminum as would the interior surface 76' of the base.The result will be that the laser beam will be reflected from the sidesurfaces and scattered by the suspended particles so that ultavioletlight of sufficient intensity to kill bacteria will reach the narrowedbottom of the flume.

All interior surfaces of all containers of each embodiment of thisinvention can also advantageously be provided with reflective surfacesto reflect the beam and take advantage of the scattering effect whichwill necessarily result from any suspended particles.

Referring now to FIGS. 8 and 9, the invention is shown incorporated intoa weir structure which includes a box-like container 80 having an inletpipe 81 and an outlet pipe 82 with an intermediate weir 83. The laser 10is mounted on one side wall of the container 80 and has its laser beam84 focused downwardly where it encounters an inclined mirror 85. Themirror reflects the beam along the upper edge of the weir 83. In theembodiment illustrated in FIGS. 6 and 7, the weir edge is horizontal andthe beam is reflected by the mirror 85 in a path which is parallel tothe horizontal top of the weir 83. A second mirror 86 may be positionedat the opposite end of the weir to reflect the laser beam to aphotoelectric cell 87 for control of the pulse rate in relation to theamount of light sensed by the photocell 87.

It will be seen that in the embodiment of FIGS. 8 and 9, thecross-section of the stream of water which passes over the weir 83 willpass through the stationary reflected laser beam 84 so that all waterpassing between the inlet 81 and the outlet 82 will be exposed to theultraviolet light.

In FIG. 10, a modification of the embodiment of FIGS. 8 and 9 is shownin which the elevation of the upper edge 88 of the weir 83' decreases asthe distance from the mirror 85 increases. The result is a wedge-shapedcross-section of water passing over the weir 83'. This wedge-shapedcross-section of the stream is selected to coincide to the change whichthe laser beam 84 undergoes as it passes through the water. That is, thelaser beam will tend to spread as it passes through the water. Themodification of FIG. 10 also takes advantage of the phenomenon that thelaser beam will be reflected back into the stream of water when itreaches the water surface if the angle of incidence at the meniscusexceeds the critical angle. This effect is illustrated by the arrow 89in FIG. 10 which shows that the laser beam will be confined within thestream of water flowing over the weir 83'. A further modification of theweir design would narrow the cross-section of the water as the distancefrom the mirror increases by increasing the elevation of the upper edgeof the weir as the distance from the mirror increases. This would be asimilar effect to that of the embodiment of FIG. 7. The embodiment ofFIG. 10 also uses a photoelectric cell 90 to sense the turbidity of thewater and to adjust the pulse rate of the laser 10 in accordancetherewith. Howver, unlike the photoelectric cell 87 in FIG. 8 whichsenses the light of the laser beam after it has passed through thewater, the photoelectric cell 90 will sense the amount of scatteredvisible light reflected off of the suspended particles in the stream.

In the embodiments of FIGS. 4-7, and 8 and 9, the container is open tothe environment. The container, whether it be the flume or weir, mayadvantageously be covered so as to exclude ambient light. Ambient lighthas the potential for including photoreactivation of the bacteria withthe result that the bacteria will be reestablished rather than bekilled.

Referring now to FIGS. 11 and 12, a further embodiment is illustratedwhich employs a spiral tube 95 having an inlet 96 at one end and anoutlet 97 at its opposite end. Water entering the inlet will be forcedto assume a spiral pattern as it passes to the outlet 97. A stationarylaser 10 having its beam focused generally along the longitudinal axisof the pipe 95 is mounted adjacent the outlet end. The outlet endincludes a transparent end wall 98 through which the beam can befocused. Inside the inlet end of the pipe 85 is a mirror surface 99which will reflect the beam back upwardly and a photocell 100 isarranged near the laser 10 to sense the amount of visible light. Again,the embodiment of FIGS. 11 and 12 employ the principal of a stationarylaser beam and a stream of water or other fluid being forced to pass thebeam. However, in this embodiment, the stream will intersect the laserbeam at multiple points along the length of the beam thereby increasingthe exposure time of the water to the ultraviolet light.

All of the embodiments thus far described have means to adjust theintensity of the laser beam by adjusting the pulse rate. It is alsopossible to adjust the geometry of the beam to adapt it to changes inconditions or characteristics of the fluid. FIG. 13 shows an arrangementto accomplish a change in the beam geometry and particularly to vary thelength (L) of the beam, that is, the smallest dimension. In thearrangement of FIG. 13, the laser 10 is mounted on a pivot 68 as in theembodiment of FIGS. 4 and 5. The angular position of the laser 10 ischanged by the pinion 70 meshing with the sector gear 69. The laser beam105 from the laser 10 is directed at a lens 106 which is a doubleconcave diverging lens. The effect of the lens 106 will be to spread thelength of the beam 105 so that the beam 105' will have an increasedlength. It is the increased length beam 105' through which the waterpasses as it is treated. The length of the beam 105' will be determinedby the angle at which the beam 105' strikes the lens 106. That angle isadjusted by adjusting the relative angular position of the laser 10.

A sensor 107, such as a Total Organic Carbon meter, is disposed in thewater being treated. The sensor 107 will produce a signal which is usedto control the operation of the motor 71 and to change the angularposition of the laser 10 as changes in the organic content of the waterare sensed. As the organic content increases, the length of the beam105' would be increased so that for a constant flow there would be agreater chance of exposure of bacteria to the ultraviolet light becauseof the increased resident time of the water passing through the beam105'. A similar adjustment may be made for changes in turbidity. Eventhough the total photons will remain the same, the likelihood of contactof bacteria will increase especially if ther is turbulent flow as thewater passes through the length of the beam 105'.

Reference has been made throughout to a gas pulsed laser as thepreferred source for the ultraviolet light. By this term I mean toinclude those lasers which are commonly known as continuous lasers butwhich have such short intervals between their pulses and such a highpulse rate that they appear to be continuous. Such so-called continuouslasers do not allow for the degree of adjustment of intensity which themore typical lower pulse rate gas laser might have. However, they couldbe used with advantage in the embodiment of FIG. 13, for example, wherethe intensity of the laser beam is held constant and the beam geometryis altered in relation to operating conditions or fluid characteristics.

It will be noted that in each of the embodiments described above, thesource of the laser beam is out of contact with the water or other fluidbeing treated. This is a significant advantage over the use ofultraviolet tubes or bulbs in which the water is typically passed overthe tubes or bulbs. Since there is no contact between the laser beamsource and the fluid, the laser source cannot become clouded or coatedby impurities in the wastewater and there is no need to continuouslyclean the apparatus.

Although nitrogen will lase and produce light in the ultraviolet range,nitrogen is not the preferred gas to be employed in the laser of myinvention. Based upon tests of a variety of eximers, it has beendetermined that the most efficient gas as measured by the amount oflight per unit of power input into the laser is achieved by using aneximer of fluorine krypton. That eximer produces a wave length of 249nanometers and tests have shown that it will exhibit about a 90%decrease in relative fecal coliform bacteria count at radiation doses of0.15 joules per square centimeter and that a 99% or more decrease isachievable at doses of about 0.3 joules per square centimeter.

The use of the laser provides a superior source of intense ultravioletradiation. As disclosed above, that source of radiation can becontrolled, adjusted and varied to produce finite disinfection by thekilling of bacteria. This is in contrast to the prior uses ofultraviolet radiation in which the radiation was simply provided ingross with the hope that the water or other fluid being treated would beexposed to sufficient radiation to be disinfected.

The flow of water through an apparatus in accordance with my inventioncan be considerably faster than that which was possible in the prior artarrangement using ultraviolet tubes or bulbs. As a result, the head lossis considerably reduced and the higher velocities tend to self-clean thesurfaces of the container through which the fluid flows. This highervelocity will also cause suspended particles to tumble. The tumblingcombined with the increased scattering of the ultraviolet lightresulting from the greater intensity of the source and the reflection ofthe laser beam off of side walls or surfaces of the container, reducesthe possibility that bacteria attached to suspended particles will notbe exposed to the ultraviolet light. Instead, all sides of suspendedparticles should receive a dose of the ultraviolet light.

The use of a laser emitting light in the ultraviolet range permits thedisinfection of fluids having a much higher turbidity than was possibleusing the tubes or bulbs involved of the prior approaches. In the methodand apparatus of my invention, some turbidity may be desirable becauseof the scattering which will result. In prior apparatus, turbidity wasalways detrimental to successful operation. The present invention alsoprovides for the adjustment of the pulse rate, the intensity, or theangle of the beam in relation to variations in turbidity.

I claim:
 1. An apparatus for disinfecting water by the exposure of thewater to light in the ultraviolet range, comprising:a water containerhaving an inlet and an outlet; means including a flume for controllingthe cross-section of water flowing between said inlet and outlet; apulsed gas laser disposed above the flume and having its beam extendingdownwardly into the flume and filling the cross-section of the water,said beam being disposed between the inlet and outlet and radiatinglight in the ultraviolet range, said laser being mounted for pivotalmovement on an axis transverse of said flume, whereby the path of saidbeam may be varied from the vertical; and means for sensing theturbidity of the water and for moving said laser to have the path ofsaid beam move from the vertical as the turbidity of said waterdecreases.
 2. An apparatus for disinfecting water by the exposure of thewater to light in the ultraviolet range, comprising:a water containerhaving an inlet and an outlet; means for controlling the cross-sectionof water flowing between said inlet and outlet; a laser having a beamwhich has a width and depth substantially filling the cross-section ofthe water without reflection from the container, said beam beingdisposed between the inlet and outlet and radiating light in theultraviolet range; and means for varying the length of said beam throughwhich the water passes.
 3. An apparatus in accordance with claim 2wherein said means for varying the length of said beam includes a lensand means for changing the distance between the laser and the lens. 4.An apparatus for disinfecting water by the exposure of the water tolight in the ultraviolet range, comprising:a water container having aninlet and an outlet; means for controlling the cross-section of waterflowing between said inlet and outlet; and a pulsed gas laser having abeam with a substantial width, the beam filling the cross-section of thewater with its width being generally transverse to the flow of water,said beam being disposed between the inlet and outlet and radiatinglight in the ultraviolet range.
 5. An apparatus in accordance with claim4 wherein said container is so shaped that said cross-section increasesin width as the width of said beam increases as it passes through thewater.
 6. An apparatus in accordance with claim 4 wherein said containeris so shaped that said cross-section decreases in width as the distancefrom the source of said beam increases.
 7. An apparatus in accordancewith claim 4 wherein said laser includes means for controlling the rateof the pulses thereof, together with flow responsive means in saidcontainer; said flow responsive means regulating the operation of saidpulse rate control.
 8. An apparatus in accordance with claim 4 whereinsaid laser includes means for controlling the rate of the pulsesthereof, together with means for sensing the visible light reflected bysuspended particles in said water and for regulating the operation ofsaid pulse rate control in response to the amount of visible light. 9.An apparatus in accordance with claim 4 wherein said means forcontrolling the cross section of water includes a flume, said laser isdisposed above said flume and said laser beam extends downwardly intothe flume.
 10. An apparatus in accordance with claim 9 together with areflective surface at the bottom of said flume which is adapted toreflect the laser beam.
 11. An apparatus in accordance with claim 10wherein said laser beam extends downwardly at an angle to the vertical.12. An apparatus in accordance with claim 4 wherein said means forcontrolling the cross-section of the water comprises a weir, and saidbeam extends generally parallel to the weir.
 13. An apparatus inaccordance with claim 12 wherein the elevation of said weir slopesdownwardly away from the source of said laser beam so that thecross-section of water increases as the distance from said sourceincreases.
 14. An apparatus in accordance with claim 4 wherein saidcontainer contains reflective surfaces for reflecting light from saidbeam and light scattered from particles suspended in said water.
 15. Anapparatus in accordance with claim 4 wherein said container is closed toexclude ambient light.
 16. An apparatus for disinfecting water by theexposure of the water to light in the ultraviolet range, comprising:awater container having an inlet and an outlet; means for controlling thecross-section of water flowing between said inlet and outlet; a pulsedgas laser having its beam filling the cross-section of the water, saidbeam being disposed between the inlet and outlet and radiating light inthe ultraviolet range; and means for sensing the visible light reflectedby suspended particles in said water and for regulating the operation ofsaid controlling means to reduce the cross-section of water as theamount of sensed visible light increases.